The product of the src gene of the Schmitt-Tuppin strain of Rous Sarcoma Virus has been shown to be a 56,000 molecular weight peptide which has an extremely short-half life (less than 30 minutes). Its action on cyclic AMP metabolism is under study. By protease treatment filamin, a phosphoprotein affected by cyclic AMP, has been converted to a form that no longer aggregates with itself but still binds to actin.